Electric valve translating circuit



April 27, 19370 H. CYPRA ELECTRIC VALVE TRANSLATING CIRCUIT Filed Jan.16, 1955 2 Sheets-Sheet 1 THERMOSTAT I IE 111 J1 I m I 11 m m 1 yr 277'277' Pig. 4.

a Inventor. 277 Helmut Cypra, 1 II III 132 y III His ttorney.

April 27, 1937. H. cYPRA ELECTRIC VALVE TRANSLATING CIRCUIT 2Sheets-Sheet 2 Filed Jan.

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Inventor": Helmut C by 11 yp a 6 ,9 His Attorney Patented Apr. 27, 1937UNITED STATES PATENT OFFICE Helmut Cypra, Berlin- Hermsdorf, Germany,assignor to General Electric Company, a corporation of New YorkApplication January 16, 1935, Serial No. 2,122

- In Germany January 19, 1934 Claims.

My invention relates to electric valve translating circuits and moreparticularly to such circuits in which the amount of current flowing inthe circuit is controlled by controlling the 5 conductivity of anelectric valve.

In the case of electrically heated furnaces it has generally beenrequired that the furnace temperature be kept substantially constantwithin very narrow limits and that it be possible to control thetemperature of the furnace by external control means. Heretofore it hasbeen common to control the temperature of the furnace by intermittentcutting in and out of heating elements by means of thermal responsiveregulating devices. Such arrangements, however, have the disadvantagethat the temperature varies between certain limits. It has beenproposed. to operate electric heating furnaces by means of grid controlrectifiers but such arrangements have not been satisfactory where thealternating current supply systemdoes not provide a neutral conductor.This generally has necessitated the use of a transformer having acapacity sufficient to carry the full output load, or it has beennecessary to provide means with an artificial neutral point.

It is an object of my invention, therefore, to provide an improvedelectric valve translating system which will overcome the abovementioned disadvantage of the arrangements of the prior art and whichwill be simple and reliable in operation.

It is another object of my invention to provide an improved electricvalve translating system in which the amount of current flowing in thesystem may be controlled by the electric valve by means of a simplecontrol circuit.

It is a further object of my invention to provide an improved electricvalve translating system for the control of electric furnaces suppliedfrom a polyphase source not provided with a neutral point.

In accordance with my invention a three-phase furnace is connected inopen or closed star arrangement wherein the individual resistors of thefurnace are connected directly with the electrodes of grid controlledelectric valves. Grid controlled electric valves each having an anodeand a cathode or a multi-anode common cathode valve can be used inconjunction with existing three-phase furnaces to provide constantreguchange in the existing furnaces.

55 The novel features which I believe to be charstar connectedmodification of my invention, and v Fig. 6 shows a closed starmodification of my invention.

Referring to Fig. l of the drawings, I have illustrated therein theapplication of my invention to a three-phase line I, 2, 3, supplyingcurrent to the resistors 4, 5, 6, of an electric furnace, the ends ofwhich are connected to the anodes of the electric valves 1, 8, and 9.The anode of each of the valves 1, 8, and 9 is connected to the cathodeof the adjacent valve so as to form a delta connection. Although any ofthe valves well knownin the art may be used, I prefer to use valvescontaining an'ionizable medium and having a control electrode. Thecontrol electrodes of the valves are energized from the three-phase linethrough any suitable phase shifting arrangement, such for example, as arotary phase shifting transformer [0 having its secondary winding llconnected to the control electrodes and cathodes of the valves 1, 8, and9. The position of the secondary windings II with respect to the primarywinding ll] of .the phase shifting arrangement is determined by thetemperature of the furnace by means of an electric motor [2 which isenergized from a thermostat IS. The thermostat l3, which is. responsiveto the temperature of the electric finnace comprising the resistors 4,5, and 6, may be any one of those common in the art which operates todetermine the direction in which the motor l2 will rotate in response toa change in the temperature of the furnace.

For a betterunderstanding of the operation of my invention reference maynow be had to Figs. 2, 3, and 4. In these figures the assumption hasbeen made that the grid control of the valve is such that an anodecurrent flows at the beginning of the cycle and the assumption alsofurthermore has been made for the purposes of explanation that thevoltage drop across the valve is negligible. For a complete cycle ofalternating current it is convenient to divide the time of the cycleinto intervals I to VI. The

curves I, 2, and 3' represent the alternating current voltage phases I,2, and 3 of Fig. 1. Thus, in time interval I current flows from phase Ithrough the discharge valve I to phase 3. It is assumed that thedischarge valves 8 and 9 are non-conductive at this instant. The dottedline curve D in time interval I thus is then the potential of thecathode of the discharge valve 1 and also of the anode of the valve 9when the load devices 4, 5, and 6 are equal and the valves 8 and 9 arenon-conductive. During the nonconductive condition of valve 8 the valve9 is at a potential corresponding to the voltage difference between thephase voltage 2' and the curve D in the first half of the time intervalI; andin the second half of the time interval I the valve 8 is at apotential equal to the voltage difference between the phase 2 and thecurve D. This causes valve 8 to become conductive so that the electrodepotentials of all the discharged valves assume the value given by theline A. Thus during the latter half of the time interval I current issupplied from the phase 2 to the resistor 5 through the electric valvenetwork. Thus each of the dotted line curves B, C, and D represents thepotentials of the discharge valves in the instance where only two phasesare active, and hence curve B represents the condition when phase 3 isinactive, curve C represents the condition when phase I is inactive, andcurve D represents the condition when phase 2 is inactive.

During actual operation in the time interval I current flows from phaseI through valve 1 to phase 3 and through the valve 9 to phase 2, and" inthe second half of the time interval I current flows from phase 2through the valves I and 8 to phase 3. It will be apparent to thoseskilled in the art that similar operating conditions obtain in the timeintervals III and V. During the time interval IV phase I is negative andhence valves 8 and 9 become conductive to transmit current to phase Ithrough the load device 4 in a reverse direction. It will furthermore beobvious to those skilled in the art that a similar cycle of operationobtains in time intervals II and VI.

If the currents flowing between two phases in the individual timeintervals are combined we may obtain the current flow through each ofthe load devices 4, 5, and 6 connected to the phases I, 2, and 3. Fig.3, therefore, represents the combination of current which indicates thetotal current and the direction thereof flowing through the loaddevices, as for example, load device 4. In Fig. 4 the currents have beencombined to produce thecurrent carried by valves, for example valve 8.It is apparent from the curve of Fig. 3 that the current does not have apredominant third harmonic present so that no harmonic is introducedinto the three-phase system. The step-like shape of the current wave andthe fact that the valves are conductive for a phase of 240 are-conduciveto the reduction of arc backs. The grid control of the valves permitsthecomplete regulation from zero to load of the furnace while maintainingthe individual phases of the system symmetrically loaded throughout thecontrol range.

While I have shown the application of my in-- vention to an arrangementwherein a threephase system supplies energy to an electric fur-- nace,it will be apparent to those skilled in the art that the resistors 4, 5,and 8 could well be the primary windings of transformers or machines.

Furthermore, it is also apparent that the arrangement is not limited tothree-phase systems but may be used with any number of phases providedthat the electric valves are connected in a polygon having as many armsor sides as there are phases. Furthermore, my invention is alsoapplicable to alternating current supply systems not provided with aneutral point.

The arrangement disclosed inFig. 5 is of particular advantage where itis desired to provide an economical arrangement for a small load orwhere it is desired to obtain economy by the use of a multi-anode singlecathode electric valve. In this figure like parts are designated withthe same reference characters as were used in Fig. i. In this instance,however, the load units or furnace heater resistors 4, 5, and 6 whichare connected to the three-phase line I, 2, 3, are connected to anelectric valve I4 to form an open star connection. a cathode, two anodesand two control electrodes. Two of the load units 4 and B are connectedto the anodes whereas the remaining load unit 5 is connected to thecathode of the valve I4. In the arrangement disclosed only two of thewindings of the phase shifting arrangement comprising the transformer I0and the secondary windings II are utilized to supply energy to thecontrol electrodes of the valve I4. It will be apparent to those skilledin tht art that the amount of power flowing-through the load devices 4,5, and 5 may be controlled by means of a shift in the phase of thecontrol electrode excitation of the valve I4 thereby controlling theamount of power transmitted between phase 2 and the remaining phases.

Fig. 6 discloses a modification which is particularly suitable for loadcircuits such as an existing threephase load or furnace having a closedstar connection where it is desired to obtain regulation withoutchanging the existing connections. Such an arrangement is alsoadvantageous where it is desired to use a multi-anode common cathodevalve for regulation and still maintain a symmetrical load on thealternating current system. Thus in Fig. 6 the load consuming devices 4,5, and Ii, which are connected to the alternating current line I, 2, 3,are joined together in star fashion to form a neutral point which isconnected to the cathode of an electric valve I5. The valve I5 isprovided with a plurality of anodes which are connected to thealternating current circuit terminals of the load devices 4, 5, and 6.Control elements or grids are provided for each of the anodes to controlthe discharge of the valve I5. The grids are energized from thealternating current line through a suitable phase shifting arrangementsuch as a rotary phase shifter comprising the transformer winding I0 andthe secondary windings II which in turn energize the windings of thetransformer I6.

The operation of the arrangement shown in Fig. 6 is such that when allof the grids or control members of the valve I5 are negative so as toprevent discharge through the valve I5 the load system or furnacecomprising the load elements 4, 5, and 6 operates as an unregulatedsystem. When one of the anodes is energized and discharge through thevalve is possible, the load device connected to that anode is shortcircuited and the output or current how in the other two load devices isincreased. The maximum output of the furnace or load circuit is obtainedwhen the grid circuit of the valve I5 is of such a. phase relation withrespect to the anode voltages as to permit complete conduction in eachcycle of alter- The valve I4 is provided with regulated from 100% toabout 240% of the normal current output of an unregulated furnace.

While the arrangement disclosed in Fig. 6 has been shown as applied to athree-phase system it will be obvious that such an arrangement can beapplied to any polyphase star connected load circuit provided thatadditional anodes and control electrodes are supplied in the controllingelectric valve.

While I have shown and described my invention in connection with certainspecific embodiments, it will, of course, be understood that I do notwish to be limited thereto, since it is apparent that the principlesherein disclosed are susceptible of numerous other applications, andmodiflcations may be made in the circuit arrangement and in theinstrumentalities employed without departing from the spirit and scopeof my invention as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In an electric valve translating system, the combination of a sourceof alternating current of n phases, n load devices each connected at oneend to a different phase, a plurality of electric valves containing anionizable medium, and

' means for controlling the conductivity of said valves, said valvesinter-connecting said load devices to provide 11 control electricdischarge paths between said devices so that the conductivity of any oneof said valves will cause current to flow through two of said devices.

2. The combination, in an electric valve trans lating apparatus, of'asource of alternating cur-= rent of n phases, 71 load devices eachconnected at one end to a different phase, 'a plurality of electricvalves containing an ionizable medium, and means for controlling theconductivity of said, valves, said valves interconnecting the other endsof said load devices so that the conductivity of any one of said valveswill cause current to flow through two of said load devices.

3. In an electric valve translating apparatus, the combination of asource of alternating current of n phases, 71. load devices eachconnected to a different phase, n electric valves connected between saidload devices and directly to each. other in a polygonal network of nsides, and means for controlling the conductivity of said valves therebyto control the current to said load devices.

4. In an electric valve translating system, the combination of a sourceof alternating current of n phases, 7; load devices arranged to form astar connected network in direct conductive relation to the phases ofsaid alternating current source, n electric valves containing anionizable medium and being connected across said load devices, and meansfor controlling the conductivity of said valves thereby to control thecurrent flow to said load devices.

5. The combination, in an electric valve translating system, of a sourceof alternating current of n phases, n load devices each arranged inconductive relation to a difierent one of said phases, a plurality ofelectric valves each containing an 'ionizable medium, and'means forcontrolling the devices whereby the conductivity of one of said

